It is known to use thread protectors to protect threaded pipe ends from damage during storage and transport. For example, U.S. Pat. No. 4,139,023 discloses a pipe thread protector which is made of a resilient material and has a cup-shaped body which overlies the pipe threads to be protected. The outermost portion of the cup-shaped body is provided with protector threads which are complementary in shape to the pipe threads. Inwardly of the protector threads, the cup-shaped body is provided with a plurality of tapered wedging ribs. These wedging ribs automatically center the cup-shaped body on the threaded pipe end as the pipe thread protector is urged over the pipe end for subsequent engagement of the protector threads with the pipe threads. The wedging ribs thereafter frictionally restrain the protector against rotation relative to the pipe end.
U.S. Pat. No. 4,553,567 discloses a protector for a threaded end section of a cylindrical part, such as a pipe, which has a tubular body having a plurality of flexible ribs projecting from a wall of the body. The ribs, in an unflexed condition, extend at an acute angle in a forward direction toward the pipe upon which the protector is placed on the threaded end section of the pipe. The body is disposed in space telescoped confronting relation to the threaded end section of the pipe to preclude circumferential and radial destructive stress between the body and the threaded end of the pipe. In one embodiment, the ribs comprise first ribs engageable with the threaded end section of the pipe and second ribs located adjacent the first ribs in holding engagement with the threaded end section of the pipe.
It is of utmost importance that thread protectors do not loosen or fall off during use and expose pipe threads. A pipe is subject to vibration loading when it is transported by a flat-bed truck or rail. Vibrations can cause prior art protectors to loosen or fall off and expose the pipe threads to severe damage. The problem is made worse under extreme weather conditions when hot temperatures cause female thread protectors to expand and cold temperatures cause male thread protectors to shrink. Changes in diameter caused by temperature fluctuations can make high-density polyethylene thread protectors extremely susceptible to disengaging from the pipe threads and vibrating loose.